The present invention relates to control apparatus and/or method for a belt drive continuously-variable transmission connected with a torque converter.
A continuously-variable transmission (CVT) of one type used for a vehicle is arranged to receive a torque from an engine through a torque converter, and to vary a transmission ratio or gear ratio continuously with primary and secondary pulleys connected by a V belt with each other. A controller for such a continuously-variable transmission calculates a target transmission ratio in accordance with a vehicle speed and a driver's accelerator input or accelerator opening degree corresponding to an accelerator depression degree, and controls the actual transmission ratio toward the target transmission ratio by controlling a fluid pressure to the primary pulley to vary contact widths of the V belt with the primary and secondary pulleys.
The controller of such a system sets a line pressure in accordance with an input torque to the continuously-variable transmission, and controls the contact frictional forces of the V belt with the pulleys with the line pressure. The line pressure, if too low with respect to the input torque, could cause slippage between the V belt and pulleys. An increase of the line pressure too high could increase a drive loss in an oil pump for producing the line pressure.
Because of the interposition of a torque converter between an engine and a continuously-variable transmission, it is not possible to sense the input torque to the transmission directly. Therefore, a control system disclosed in a Japanese Patent Application Publication H01(1989)-206155 is configured to measure a torque converter input revolution speed (=engine speed Ne) and a torque converter output speed (=primary pulley speed Np); to calculate a torque converter speed ratio (=output speed/input speed) e from the measured torque converter input and output speeds; and to estimate an input torque Tat to the continuously-variable transmission by using a speed ratio versus torque ratio map representing a relationship between the speed ratio e and a torque ratio τ of the torque converter.